1. Field of the Invention
This invention relates to a single use applicator for applying viscous fluids having viscosities greater than water, and is of the type which includes fluid carried in a hermetically sealed crushable glass ampoule, with an anhydrous inert gas head, which ampoule is contained in a chemically inert deformable tube, with an application element comprised of a plurality of synthetic fiber strands bonded thereto. The application element has a centrally located restrictive valve section to control fluid flow, with an internal fluid reservoir section adjacent the ampoule, and an external tip section to apply the fluid.
2. Description of the Prior Art
Applicators for dispensing fluids for various uses, and which are of the single use type are well known in the art. Such applicators take many forms, but the most common device is one that contains a thin walled glass ampoule that contains fluid, which ampoule is inside a cardboard or plastic tube which is closed at one end and sealed at the other end with a porous application tip. Various techniques are used to release the fluid from the ampoule, including crushing the tube with the thumb and forefinger, a slide ring activator to crush the ampoule as described in the Frazier U.S. Pat. No. 5,509,744, or using an external lever or an integral plunger to the tube, as described in the Koreska U.S Pat. No. 4,784,506. Most of the prior art patents deal with fluids of relatively low viscosity (i.e. equal to or less than water or that are generally described as “ideal fluids”) that readily flow in the tube to the fibrous applicator tip and saturate the tip. The applicator tip in these devices is generally designed so that it can totally hold, or absorb the fluid contained in the ampoule, so that dripping is not a concern. This design technique, however, allows a significant quantity of the dispersed fluid to remain in the tip after use, thereby reducing the efficiency of the device and also limiting the amount of fluid to be dispensed.
When attempting to fill the prior art devices described above with fluids with higher viscosities than water, and in quantities greater than the saturation capacity of the absorbent tip, the flow rate of the fluid to the application tip is considerably longer in time than efficiency will allow for convenient and effective use. Additionally, when these prior art applicator devices with an application tip saturated with the application fluid are held in the downward position, the unabsorbed fluid above the saturated porous application tip creates hydrostatic head pressure, which is directly proportional to the fluid height above the tip, and will cause the applicator to drip fluid from the tip at first and then slow down as the hydrostatic head is reduced, thereby creating a non uniform fluid application.
Non-uniform fluid application is particularly abhorrent when applying adhesion promotion primers to metal, glass or other hard surfaces. Applying too much primer is worse than no primer at all, as a very uniform and thin layer of primer is always desired.
In the prior art Andrews U.S. Pat. No. 3,393,962 fluid flow to the application tip is prevented unless the user squeezes the device. A series of chambers and communication tubes is used to achieve this result. In addition, the '962 device requires the use of a pre-filter, making the device costly to assemble. Proper use of the device relies heavily on the user's ability to squeeze just the right quantity of fluid to the brush tip through finger pressure on the tube. Too great a squeeze pressure will cause the applicator brush to drip, or cause too much, or varying amounts of fluid to be applied to the surface. Using the Andrews device in an inverted upward position to apply a uniform application, is particularly difficult, if not impossible, as a constantly increasing finger tip pressure would be required to apply a uniform band of the application fluid.
Robert in U.S. Pat. No. 1,146,522 tried to solve the problem of reducing the time to saturate the tip by encapsulating the brush tip within the liquid filled ampoule. Depending on how the device was stored prior to activating (i.e. tip up or tip down), non uniform results are obtained as the tip is very likely to drip if stored with tip down, and if stored with the tip up prior to activating, the fibrous tip is likely to be dry of most fluid, and the user would be back to the long time frame required for the tip to “wet out”. Since the body housing the '522 device is not deformable (because it is glass) reducing the “wet out” time of the brush tip by squeezing the body housing is not possible. Finally this device exposes the ampoule to accidental breakage prior to use since it is housed in an unprotected glass body.
Krawczyk in U.S. Pat. No. 6,039,488 does not deal with the issues presented by dispensing and applying “non-ideal” fluids with viscosities higher than water, or with the fluid content of the encapsulating ampoule being in excess of the saturation level of the application tip, (or holding capacity) of its porous plug construction. For a device to effectively deal with the above conditions, the applicator must have an internal valve feature, ideally located at the approximate mid-point of its porous element, and having a narrowing cross section of the deformable tube. My device uses a three sectioned porous element. One, a middle or valve section of higher porous density than either of the two ends. The density of this valve section is chosen to give the desired flow rate of the specific application fluid to be used. The internal end section of the porous element, which has a substantially lower density than the valve section, acts as a fluid reservoir that is in immediate and adjacent contact with the valve section of the porous element. The external end section of the porous element also has an equally lower porous density and acts as a soft, compliant applicator tip.
The '488 patent only provides a “porous plug” with or without “small passage ways” that necessarily would have a uniform linear density along the porous plug length. To attempt to apply fluids in excess of the saturation level of the porous plug, would, from time to time, necessarily allow too much, or too little fluid to be applied to the surface to be primed, as the hydrostatic pressure head above the porous plug would vary as the fluid level changes, as it is being dispensed. Assuming the porous plug's density was chosen to allow the desired flow rate to the outer end of the applicator, any fluid in excess of the saturation level of the plug that is above the plug would create a varying hydrostatic fluid head pressure. This condition, at the beginning of use, would cause excessive flow to the tip (and perhaps cause dripping). Proper flow would only be restored after this excess fluid was dispensed. This same situation would occur when dispensing fluids with viscosities greater than water, when the applicator was in a vertically downward position. However, when used in an inverted upward position, the flow rates would fall off dramatically since the porous plug would be starved for a continued flow of fluid as the '488 structure makes no provision for an internal and adjacent reservoir section (with lower porous density) as part of the porous plug. Moreover, the user would have to squeeze the applicator to increase flow, and excessive fluid laydown could result. If used in the tip down configuration, there is no way to slow down the fluid flow once the uniform density of the tip is chosen for the design. If the density of the tip is chosen so as to allow a certain flow rate while there is a hydrostatic head pressure over the tip (i.e. at the start of use of the device), the flow will necessarily be inadequate when this hydrostatic head is reduced or absent. To increase the flow in the '488 device would require the unreliable technique of squeezing the tube to restore fluid flow.
The device described in the Fisher U.S. Pat. No. 5,746,019 is subject to the same limitations as the Krawczyk device. Wirt in U.S. Pat. No. 5,288,159 does not allow use of ‘non-ideal’ fluids (i.e. fluids with viscosities greater than water) since there is no way to speed up “wet out” times. The '159 device has an air vent in the top, so that squeezing the tube to increase the internal pressure above the fluid, even if possible, would not force the viscous fluid through the applicator pad. Additionally, since there is not internal fibrous reservoir next to the applicator pad, to “feed” fluid via capillary action, the device cannot be used effectively for inverted and upward operational positions.
Schwartzman in U.S. Pat. No. 3,614,245 does not deal with applying larger quantities of viscose application fluid in excess of the saturation capacity of the surrounding porous material. Fluid is dispersed in all directions making the device inefficient, as a large portion of the application fluid will remain in the device as absorbed fluid, and undeliverable to the open end of the applicator. In the case of very expensive viscous fluids, to overcome this characteristic of the '245 device would require filling the ampoule with excessive fluid, causing the device's cost to be uneconomical.
The single use applicator of the invention allows viscous fluids to be applied with a thin uniform application of the fluid to the application surface, and does not suffer from the prior art problems.